1. Field of the Invention
This invention relates broadly to compositions and method for stabilizing polymers. In a preferred embodiment, the invention relates to stabilization of bioadhesives and viscosity enhancers in ophthalmic compositions.
2. Description of the Related Art
Water soluble and water swellable (i.e., hydrophilic but water insoluble) polymeric materials are known to be useful as bioadhesives and viscosity enhancers. For example, poly(acrylic acids) are used in ophthalmic solutions or mixtures to increase viscosity, thereby increasing the retention time in the eye. An example of a commercially available viscosity enhancer is NOVEON.TM. AA-1 resins (polycarbophil) available from B. F. Goodrich.
Typically, polymeric viscosity enhancers and bioadhesives decompose, or are otherwise altered, during extended storage periods. The decomposition of a viscosity enhancer reduces the viscosity of the composition, eventually to a point at which the composition is no longer deemed sufficiently effective. Thus, there exists shelf-life problems with compositions, most notably ophthalmic compositions, which include bioadhesives and viscosity enhancers. Accordingly, there is a need to reduce the rate of decomposition of bioadhesives and viscosity enhancers, and to increase the shelf life of compositions including these polymeric materials.